1. Field of the Invention
This invention relates to admixing liquid components and to apparatus for carrying out the admixing and is more particularly concerned with an improved apparatus for mixing liquid components which enter into rapid chemical reaction immediately upon admixture.
2. Description of the Prior Art
Certain chemical reactions which are routinely carried out on a commercial scale pose a very serious problem because of the speed with which the reaction takes place after the reactants are brought together. The efficiency of mixing of such reactants is of critical importance in carrying out the desired reaction. Thus, if the mixture of reactants is not homogeneous when the reaction commences there will be variation, from site to site within the reaction mixture, of the relative molar proportions of the reactants. Such variation can lead to the formation of different products at the different sites.
The reaction between phosgene and polyamines to form polyisocyanates and the reaction between aniline and formaldehyde, usually in the presence of hydrochloric acid, to form methylene-bridged polyphenyl polyamines, are two such reactions. In both of these reactions the initiation of reaction after admixture of the reactants is almost instantaneous. Further, inefficient admixture of the reactants can give rise in both cases to the formation of solid by-products which tend to separate as they are formed. Such deposition can, in certain circumstances, lead to clogging of apparatus and eventually to shutdown of the reaction process.
Much attention has been paid in the prior art to the particular problem of seeking to minimize the effects of solid deposition in carrying out the above types of reaction. Thus, the use has been reported of a rotary mixer with high shear mix zone (U.S. Pat. No. 3,781,320), of a high speed mixer (U.S. Pat. No. 3,188,337), and of a multi-stage rotary pump (U.S. Pat. No. 3,947,484). The latter reference gives a lengthy analysis of the various prior art methods which have been utilized for this type of reaction and the analysis in question is hereby incorporated in this disclosure by reference.
One of the most successful devices hitherto employed in the art for carrying out the above reactions is that described in U.S. Pat. No. 3,507,626 and the improvement thereof which is described in British Pat. No. 1,238,669. In the latter reference a device is described by means of which the two streams of reactants are caused to follow initially parallel annular paths one of which ultimately flares outwardly and is united with the other, the mixed fluids being carried rapidly downstream from the point of mixing so that backmixing and deposition of by-product solids at the site of mixing are both minimized. It has been found, however, that even the use of this device gives rise eventually to the buildup of layers of solid on the walls of the mixing device adjacent the point of admixture of the two reactant streams. This leads to channeling of product in the mixing device and ultimately requires that the device be taken out of service for cleaning and repairs.
We have now found that the problems hitherto encountered in the art in the efficient admixing of highly reactive components can be minimized or eliminated using the novel apparatus and process which are described hereinafter. Further, we have found that the increased efficiency of mixing of the reactants which is achieved by the process and apparatus herein described, results in production of end product of improved properties not all of which appear to be attributable solely to the more efficient mixing of the starting reactants.